The signal processing gain by digital beamforming in Doppler sonar was investigated in terms of the enhancement of signal‐to‐reverberation ratio (SRR) at the postbeamforming Doppler‐filter output with an objective to determine the minimum number of bits necessary for the quantization of beamformer channel input signals without appreciable degradation of sonar performance. The formulation of the problem follows closely the author’s earlier work which extends Davenport’s analysis of bandpass limiter to the more general multichannel multibit signal processors. Owing to the Doppler shift of target signal frequency and the relatively narrow bandwidth of Doppler filters, we express the frequency selective effect in the nonlinear interacting power series in terms of a new set of coefficientscmk, which bear crucial significance in sonar performance. Extensive numerical calculations of ’’Doppler processing gain’’ were carried out to demonstrate that four‐bit quantization of array transducer signals is theoretically sufficient to yield a performance essentially identical to that of a linear beamformer, but severe loss of gain could result if fewer than four bits are taken at the quantizer output. It is further demonstrated numerically and substantiated analytically that, for small input SRR, the processing gain of a digital beamformer with Doppler filters cannot exceed that of a linear (or optimized four‐bit digital) beamformer even it its channel signals are quantized into more than four bits.